CHARACTERIZATION OF POST TRANSCRIPTIONAL GENE SILENCING SUPPRESSOR PROTEINS OF BENYVIRUS

An innate mechanism that plants use to protect themselves against viral infections is called Post Transcriptional Gene Silencing (PTGS). PTGS is triggered by the presence of aberrant RNA or dsRNA generated during the replication of viral genomes and leads to their degradation. To counteract this innate mechanism, viruses co-evolved with their hosts and express viral suppressors of RNA silencing (VSR) that inhibit the PTGS. . The properties of the Benyvirus VSRs have been investigated. Such VSR consist of cysteine-rich proteins (CRP) of 14kDa expressed from RNA2 of both benyvirus species used in this study. The CRPs have a zinc-finger domain able to bind nucleic acids. Agroinfection of Nicotiana benthamiana plants demonstrated that these proteins are able to suppress the PTGS downstream of the Dicer proteins, without interfering with the transitivity. Both p14s are localized in the nucleolus and in the cytoplasm in and out of the viral context. Moreover yeast two-hybrid and three-hybrid tests proved that these proteins form homodimers and bind the “coremin” sequence, a stretch of 20 nucleotides present in the RNA-3 of both viruses and necessary for the systemic spread of the virus in the plant. Some of the investigation performed to elucidate the existing connection between the p14s and VSR activity, the “coremin” sequence and the long distance movement of Benyviruses will be presented.